Source side harmonics detection and compensation in commercial substation.
The Harmonics is one of the components that affects power quality in both residential and commercial buildings and can cause serious malfunctioning and even damage to today's highly sophisticated electrical and electronic equipment . The distortion components can be submultiples of the fundamental frequencies in a power system and cause distortion in the sinusoidal wave shape and are called harmonic distortion but generally the integer multiples are referred as harmonic components and are harmonic distortion.
The current and voltage waveforms are different in harmonic components. These equipments are highly sensitive to power distortions since all the loads that are being used are of non linear in nature. Harmonic distortion is the one playing the major role among them. In any electrical network, these harmonics cause an increase in system current, voltage ratings resulting in heating. This is one of the reasons for component malfunction. Harmonic distortion is a measure of the amount of power contained in the harmonics of a fundamental signal . The harmonic distortions are inbuilt in the system with non linear characteristics. The more nonlinear, the greater is its harmonic distortion. In general, harmonic distortion plays a major role in affecting the power quality measures of the power system .
The figure 1.1 represents the conceptual block diagram of the proposed system in which the three phase supply from the power system is being fed through the inductors from the source side [L.sub.SA], [L.sub.SB], [L.sub.SC], to the control block. The control block consists of the inputs, feedback and the output. The output of the control block is given to the shunt active power filter block. The shunt active power filter block consists of a six switching devices that is IGBTs connected in parallel to each other driven by [V.sub.D] . The output is given to the non-linear load and on analyzing; it is found that there is reduction in the harmonics level since the shunt active power harmonic filter being used is obtained.
In order to be able to analyze complex signals that have many different frequencies present, a number of mathematical methods were developed. One of the more popular is called the Fourier Transform. Duplicating the mathematical steps required in a microprocessor or computer-based instrument is quite difficult. To analyze the THD, Fast Fourier Transform (FFT) or Discrete Fourier Transform (DFT) is used. These methods only work properly if the signal is composed of only the fundamental and harmonic frequencies in a certain frequency range.
The generation and detection of the harmonics in the source side of the power system and the respective steps to mitigate the effects of harmonic distortions are given. The various types of filters that are being used for the conventional method is also discussed and improvement in it is made to obtain the desired output.
i) Harmonic Compensation Techniques:
Harmonic producing load such as diode or thyristor converter or Cyclo converters have been serious problem to solve since it creates interference in power system. Passive filters usually a bank of tuned LC filters because of low initial cost and high efficiency have been broadly used to suppress harmonics. But the tuned LC creates a resonance between a source and filter causes amplification of harmonic currents on the source side at specific frequencies. Also these filters fall into series resonance with source so that voltage distortion produces excessive harmonic currents flowing through this filter. With progresses in power electronics devices, active filters consisting of voltage or current source PWM inverters have been studied and put into practical use because they have the ability to overcome the disadvantages caused by passive filters.
ii) Drawbacks In The Existing System:
Fourier transform which converts only time domain waveforms into their frequency components requires more computations and computational time. Passive filters attenuate specific harmonic frequency at the system dependent. In the case of further expansion if the system in the future it requires retuning or resizing of the filter. Since passive filters are combination of tuned series capacitors and inductors there exists another attenuating method called inductive reactance which consists of line reactor or isolation transformer. It is used only to attenuate higher order harmonics.
2 Proposed System:
In our proposed system, the main drawbacks of the existing systems which makes the availability of amplitude and phase of the fundamental and harmonics present in the signal is eradicated. The computation can be made in both frequency and time domain by using the Fast Fourier Transform Algorithm to detect the harmonic presence with the calculation made in Decimation in time domain method for the fast computation. The THD value calculated for the computation has been compared with the output of Shunt Active filter installed after the detection to reduce the harmonics . Thus the simulink model has been employed in MATLAB R2016a to design the Shunt active filter and to get the desired result at the load of the substation.
The circuit diagram of shunt active power filter is shown in the figure 1.2. The active power filter consists of three main sections that include power grid, filter section and the load side. In which the source is taken from the power grid is to be subjected for harmonic analysis . The active power filter is made of IGBT technology which is in parallel with the capacitor to get the compensation current to feed the input to get the desired result. The output from the shunt active power filter is enough to excite the loads connected to the system with low harmonic losses .
The figure 1.2 represents the Simulink model of implementing the shunt active power filter through FFT analysis . The three phase source is considered as the power grid of 110KV substation with some harmonics at the source side is to be mitigated with the shunt active power filter.
The shunt active power filter is controlled by the hysteresis controller to get the output signals in both current and voltage waveforms. IGBT Diodes are connected in parallel to each other. The current values compared with the source and the reference readings to get the actual load current . The filtered voltage from the active filter is fed to three phase Voltage Current Measurement block to activate the thyristor diodes that are connected in parallel with parallel RL load.
2.1 Experimental System Parameter:
Source Voltage [V.sub.s] = 4160 V
Source Resistance, [R.sub.s] = 0.1 ohm
Source Inductance, [L.sub.s] = 0.05Mh
DC Capacitance = 4700[micro]F
Load Resistance, [R.sub.L] = 100 ohm
Load Inductance, [L.sub.L] = 20Mh
Sample Time, [T.sub.s] = 2[micro]s
RESULTS AND DISCUSSIONS
3.1 Harmonics Outcome:
Harmonics is reduced in this technique by using the shunt active filter, which is used to reduce the frequency level of both the systems . Thus it is used for reducing the harmonics by using the Total Harmonic Distortion (THD) method by which we gain the two voltages of the system in a reduced form and the hardware reads the voltage, frequency of the system.
3.2 Software Results:
3.2.1 Voltage before Compensation:
The above Figure 2.1 represents the voltage waveform before compensation. The amplitude is taken in the X-Axis and the time period is taken in the Y-Axis. It can be seen that there are many distrition in the waveform. The waveform corresponds to the three phase R, Y, B of the circuit. The voltage range varying from +3000 volts to -3000 volts. The time period is scaled in seconds 0.02 intervals. The waveforms shows the distortions clearly.
3.2.2 Voltage after Compensation:
The figure 4.2 represents the output waveform of voltage after compensation with is obtained using filter that is shunt active filter. The amplitude is taken in Y-axis in the range of +3000 to -3000 volts. The time is denoted in the X-axis in the 0.02 seconds. It could be seen that the complete sinusoidal waveform is obtained. The THD is completely reduced.
3.2.3 Current before Compensation:
The Figure 2.3 explains the output waveform of the current before compensation of the three phase supply. The X-axis consists of the amplitude in the range of +30 volts to -30 volts. Time period is taken in the Y-axis in the range of 0.5 seconds. The distortions in the system are taken into considerations.
The R, Y, B phase sequence from the input is shown in the figure with distortions. The waveform thus obtained is not a pure sinusoidal wave indicating presence of harmonics in the system there by increasing the THD level of the entire power system.
3.2.4 Current after Compensation:
The Figure 4.3 completely explains about the output waveform of current that is being obtained by using shunt active filter simulated in MATLAB Simulink. It may be noted that a sinusoidal wave with a less or no distortion is obtained.
The figure depicts the three phase supply of R, Y, and B. The amplitude is taken in the X-axis where as the time period is taken in the Y-axis. The total harmonics distortion is reduced very much.
3.2.5 THD Calculation For Current Without Filter:
The Figure 2.5 depicts the Total Harmonics Distortions that is present in the source side of the given existing system before using the filter. It can be seen that the harmonics level is about 14.91%. The magnitude is taken in the [X.sub.axis] and the Frequency is taken in the Y-axis. The Start time is set to 0. The Number of Cycles is 5. The maximum frequency for THD computation is Nyquist frequency. The Maximum frequency range is set to 1000.
3.2.6 THD Calculation For Current With Filter:
The Figure 4.6 represents the THD calculation that was carried out using FFT analyzing tool in MATLAB Simulink after compensation. The syntax is being fed to the MATLAB m file and the file is then imported. The Number of Cycles is set to 5. The Maximum Frequency is about 1000. The Maximum frequency for THD calculation is Nyquist frequency. The frequency is taken in the X-axis and the magnitude is taken in the Y-axis. The THD is calculated by the FFT analysis and it is found that it has been reduced and ranges in the order of 1.70%. Thus the THD has been reduced to a great extend since the active harmonic filters are being used.
3.2.7 THD Calculation For Voltage Without Filter:
The figure 2.7 represents calculated value of THD using FFT Algorithm in the Simulink model without using filter before compensation. It can be seen that the value of THD is in the range of 14.91%. This may cause harmonics and it related problems in the power system. The respective steps are being taken to mitigate the THD level. The number of cycles are taken as the same 5 like the before THD calculations. The maximum frequency is set to 1000 Hertz. The display is in the form of bar relative to fundamental frequency. The bar chart represents the corresponding output for odd order harmonics like 3, 5, 7, 9.
3.2.8 THD Calculation For Voltage With Filter:
The figure 4.8 represents the calculated THD value for voltage using FFT Algorithm in the MATLAB Simulink after compensation using shunt active filter. It is clear that the THD value is reduced to 0.01%. This is achieved by using the shunt active filter. The number of cycles is set to 5, with the maximum frequency of about 1000. The output is displayed in bar chart related to fundamental value which represents the odd order harmonics. The complete sinusoidal waveform is obtained after usage of the filter indicating the reduction in the total harmonic distortion.
3.3 Current Compensation:
The table 2.2 explains the current compensation readings for various orders of odd harmonics and their corresponding readings of without filter and with filter are noted down and represented. It could be noted that the value of the total harmonic distortion is of higher percentage without using filter . When filter is being used, in the case of using shunt active filter as proposed in the project the percentage of total harmonic distortion is less than one percent, thereby ensuring safer operation of the equipment.
Thus the overview of the project and the survey about the various literatures has been undergone. The existing system in practice and the traditional methodology for the detection and compensation of the harmonics is discussed. The proposed system is designed in such a way that it overcomes the drawbacks of the existing system. Thus it mainly focuses on the software output. The entire project is being simulated in Simulink tool in MATLAB R2017b. The corresponding waveform of the Simulink model before compensation and after compensation which is done using shunt active filter is discussed and the results are inferred. On examining the obtained results it can be concluded that the usage of shunt active filter can reduce harmonics to a greater extent. The THD thus obtained before compensation and after compensation is analyzed to infer the required results. In order to conclude the system it is enabled to reduce the harmonic defects using the Total Harmonic Distortion (THD) in the source side of the 110kV substation which has been detected by FFT Algorithm and compensated by using the Shunt Active Filter. The Outputs of the system is simulated and the voltage and the current waveforms are obtained. The Results shows the performance of the system is improved by reducing the harmonics and the Total harmonics distortion is very much reduced(less than 1%) and lies within the IEEE limits.
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(1) Maheswari C, (2) Dr Rani Thottungal, (3) Santhiya R
(1) Maheswari C, AP/EEE, Dr.N.G.P Institute of Technology, Coimbatore, Tamilnadu, India,
(2) Dr Rani Thottungal, Prof & Head/ EEE, Kumaraguru Institute of Technology, Coimbatore,
(3) Santhiya R, AP/EEE, Dr.N.G.P Institute of Technology, Coimbatore, Tamil Nadu, India,
Received lApril 2017; Accepted 18 June 2017; Available online 2 July 2017
Address For Correspondence:
C.Maheswari, AP/EEE , Dr N.G.P Institute of Technology,Coimbatore-641048, Tamil Nadu. E-mail: firstname.lastname@example.org
Caption: Fig. 1.1: conceptual block diagram of shunt active filter
Caption: Fig. 1.1: Circuit diagram of shunt active filter
Caption: Fig. 1.2: Simulink model of shunt active filter
Caption: Fig. 3.1: Output Voltage before Compensation
Caption: Fig. 3.2: Output Voltage after Compensation
Caption: Fig. 3.3: Output current Before Compensation
Caption: Fig. 3.4: Output current Before Compensation
Caption: Fig. 3.5: THD Calculation for current Using FFT in MATLAB Simulink (Before Compensation)
Caption: Fig. 3.6: THD Calculation for current Using FFT in MATLAB Simulink (After Compensation)
Caption: Fig. 3.7: THD Calculation for Voltage Using FFT in MATLAB Simulink (Before Compensation)
Caption: Fig. 2.8: THD Calculation for Voltage Using FFT in MATLAB Simulink (After Compensation)
Table 3.1: Fast Fourier Transform Readings x(n) Voltage in KV x(n) (in normal order) (in reversed order) x(0) 109.5 x(0)=109.5KV x(1) 108.3 x(4)=108.9KV x(2) 108.0 x(2)=108.0KV X(31 107.6 x(6)=106.5KV x(4) 108.9 x(1)=108.3KV x(5) 109.0 x(5)=109.0KV x(6) 106.5 x(3)=107.6KV x(7) 104.3 x(7)=104.3KV Table 3.2: Current compensation reading. Order of Harmonics Without Filter With Filter 3 0.25% 0.18% 5 8.43% 1.04% 7 4.53% 0.31% 9 0.25% 0.07% 11 4.15% 0.18% 13 2.90% 0.12% 15 0.26% 0.03% 17 2.45% 0.11% 19 1.95% 0.08%
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|Author:||Maheswari, C.; Thottungal, Rani; Santhiya, R.|
|Publication:||Advances in Natural and Applied Sciences|
|Date:||Jul 1, 2017|
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